Sub-Nanosecond Time Measurement utilizing a Continual Fraction Divider
In the realm of electronics, detecting signal pulses with picosecond accuracy presents complex challenges. One such challenge is the time-walk effect, where stronger signals can appear to arrive faster due to amplitude-dependent threshold crossing. To overcome this issue, Michael Wiebusch introduced a budget-friendly implementation of a constant-fraction discriminator (CFD), which triggers at a constant fraction of the signal pulse, mitigating the time-walk effect.
A CFD divides an input signal into two separate components. One component is inverted, attenuated, and delayed, while the other is left untouched. The recombination of these two parts results in a sum that crosses zero at a consistent fraction of the original pulse amplitude, which can be more readily detected by processing circuitry. This zero-crossing detection method provides a more accurate timing solution compared to simple voltage threshold checks.
Unfortunately, traditional CFDs utilize expensive, high-speed operational amplifiers for quick pulse processing. Wiebusch's design addresses this issue by using affordable integrated circuits, transistors, resistors, capacitors, and a coaxial cable as a delay line. The resulting circuit boasts a timing precision of 60 picoseconds, ideal for high-precision timing tasks such as gamma-ray spectroscopy or photomultiplier tube (PMT) signal processing.
The main drawback is that the circuit is tailored to specific signal pulse lengths. However, it can be easily adapted for other pulse shapes by adjusting the cable delay and attenuation fraction accordingly.
This CFD design was devised for a gamma-ray spectrometer, a device that processes signals from photomultiplier tubes or scintillators, as seen in earlier examples.
Michael Wiebusch's CFD design provides an accessible, affordable, and effective solution for achieving precise timing in the picoseconds domain. The design process is documented in an open-access paper and detailed in several recent electronics maker articles, making it accessible to enthusiasts and researchers in search of a budget-friendly, precision timing solution.
The circuit design by Michael Wiebusch employs affordable electronics components, such as integrated circuits, transistors, resistors, capacitors, and a coaxial cable, to create a constant-fraction discriminator (CFD) that addresses the issue of expensive operational amplifiers in traditional CFDs. This budget-friendly CFD design, documented in an open-access paper and electronics maker articles, can be a valuable asset for people interested in DIY electronic projects, particularly those focusing on high-precision timing tasks like gamma-ray spectroscopy or photomultiplier tube (PMT) signal processing.
